COVID-19 Lecture Notes

COVID-19

Introduction

• SARS-CoV-2 emerged in late 2019.
• Caused a global pandemic.
• COVID-19 clinical presentation ranges from asymptomatic to severe ARDS (Acute Respiratory Distress Syndrome).
• WHO declared an end to the public health emergency in May 2023.

Virology and Variants

• SARS-CoV-2 is a betacoronavirus.
• It uses ACE2 for cell entry.
• Variants like Alpha, Delta, and Omicron show different transmissibility and immune evasion.
• Omicron sublineages dominate due to replication advantage in upper airways.

Epidemiology

• High transmission occurs in congregate settings and among vulnerable populations.
• Transitioning from pandemic to endemic status.
• Over 15 million excess deaths estimated in 2020–2021.

Clinical Spectrum of COVID-19

• Ranges from asymptomatic to critical illness.
• 20–40% of infections are asymptomatic.
• Omicron variants generally associated with milder illness.

Common Symptoms

• Initial symptoms: nasal congestion, cough, sore throat, fatigue.
• Fever is not always present at onset.
• Gastrointestinal (GI) symptoms in approximately 18%: diarrhea, nausea, abdominal pain.

Clinical Classifications

• Mild: No hypoxia or abnormal chest imaging.
• Moderate: Lower respiratory symptoms, SpO_2 \geq 94\%. (This indicates the patient's oxygen saturation is greater than or equal to 94%)
• Severe: SpO_2 < 94\%, >50% lung involvement, tachypnea. (This indicates the patient's oxygen saturation is less than 94% and there is more than 50% lung involvement.)
• Critical: Respiratory failure, septic shock, or multiorgan dysfunction.

Risk Factors for Severe Illness

• Advanced age (especially \geq 65 years).
• Immunocompromised states, comorbidities (e.g., diabetes, heart disease).
• High viral load, lack of antibody response.

Complications

• ARDS is the major complication in severe cases.
• Cardiac issues: arrhythmias, myocarditis, shock.
• Thrombosis: DVT (deep vein thrombosis), PE (pulmonary embolism), stroke, arterial events.

Long COVID and Sequelae

• Persistent symptoms >4 weeks after infection.
• Common symptoms: fatigue, dyspnea, memory problems.
• Can involve respiratory, cardiovascular, neurologic systems.

Special Populations

• Children: typically mild, risk of MIS-C (Multisystem Inflammatory Syndrome in Children).
• Pregnant women: same approach as nonpregnant individuals.
• HIV patients: similar presentation, higher risk of severe outcomes.

Diagnosis of COVID-19

• Clinical suspicion based on respiratory and systemic symptoms.
• NAAT (RT-PCR) preferred for diagnosis due to high sensitivity.
• Antigen tests useful for rapid testing, especially in community settings.

Testing Indications

• Test symptomatic individuals with implications for treatment or infection control.
• Test selected asymptomatic individuals after known exposure.
• Serial testing useful in outbreak and congregate settings.

Outpatient Management

• Stratify patients by severity: mild, moderate, or severe.
• Mild cases managed via telehealth with symptom monitoring.
• Moderate to severe cases may need in-person or emergency care.

Therapeutics

• Initiate treatment early in high-risk outpatients.
• Options include antivirals like nirmatrelvir/ritonavir (Paxlovid), remdesivir.
• Monoclonal antibodies are less used due to variant resistance.

Vaccines: Overview

• Vaccines are key to reducing severe disease and mortality.
• mRNA (Moderna, Pfizer) and protein-based (Novavax) vaccines are used.
• Current formulations target Omicron variants.

Vaccine Recommendations

• CDC recommends vaccination for all individuals \geq 6 months.
• High-priority groups: elderly, immunocompromised, comorbid conditions.
• Boosters updated for circulating variants (e.g., KP.2 in 2025).

Conclusion

• COVID-19 remains a critical health issue despite lower mortality.
• Vaccination, early diagnosis, and outpatient triage are central to management.
• Continuous surveillance and variant adaptation remain vital.